The long term objectives of this research plan have been to describe the anatomical details of the specific pathways from dental structures to brain stem, emphasizing central (CNS) sites of representation, and to delineate the morphologic effects of tooth loss or dental lesions. Light and electron microscopy (LM and EM) in cats during tooth shedding or following dental lesions and in monkeys after dental surgery are being used to study the trigeminal system, with emphasis on the brain stem trigeminal nuclei (TNC). Special attention is being given to axonal and synaptic patterns and alterations in these structures after tooth loss or dental surgery, both of which show different forms of transganglionic degeneration. Conventional LM and EM studies of such transganglionic degeneration are being supplemented by studies of transganglionic transport of horseradish peroxidase (HRP). Transganglionic degeneration (after dental lesions) and transganglionic transport of HRP (put in tooth pulps) have shown two different patterns of afferent distribution within TNC for adult cat. Degeneration from teeth occurs in mid-ventral regions of partes caudalis and interpolaris, whereas HRP from teeth is transported to the dorsal and medial regions of all the subnuclei of TNC. This unexpected "dual pattern" of projection is to be investigated by use of toxic Ricin. ricin causes selective death of the sensory ganglion cells of the nerves exposed to it and a resultant transganglionic CNS degeneration. Ricin will be used in adult cats, kittens at various ages of tooth eruption and in adult monkeys (in conjunction with LM-HRP transport studies in the kittens and monkeys). Full quandrants (maxillary and mandibular) and individual teeth (canines) will be used in each model to compare and contrast CNS patterns of projection and especially to delineate the apparent plasticity occurring during tooth shedding in kittens. The occaasional variable results obtained by dental lesions (especially of single teeth) will be alleviated here as Ricin causes extensive central degeneration. The limitations of this relatively new procedure will be determined. The experiments are designed to readily yield fresh data directly related to this dual CNS projection specifically from teeth, and to test the possibility of a normal plastic CNS reorganization associated with natural tooth shedding.